The present invention relates to a method and apparatus for breaking up and separating waste glass for the reuse of the waste glass as a regenerated material, namely as cullet.
Recycled waste glass contains aluminum, iron, synthetic resin, cork and like caps for glass bottles. Waste glass may further contain empty cans of aluminum, iron and other materials. When such waste glass is used as cullet, the glass product obtained contains bubbles and unmelted substances, i.e. so-called "stones," and involves changes in color or refinement due to the presence of various kinds of extraneous matter. These objections reduce the strength and appearance of the product, seriously impairing the commercial value of the product.
Accordingly the extraneous matter must be removed to the greatest possible extent. However, the extraneous matter varies greatly in shape and properties. Moreover, regardless of whether the waste glass has been fractured or not, some kinds of extraneous matter may not differ from the waste glass in shape, size or specific gravity. Thus the undesirable matter is not readily separable by the conventional methods such as screening, washing with water, sink and float separation, etc., with the exception of magnetic materials which are magnetically separable. In fact the conventional methods give very low yields.
FIG. 1 is a flow chart showing a conventional process generally practiced for removing extraneous matter from waste glass. With this process, recycled waste glass is first manually roughly broken in order to fracture glass articles which are almost in complete shape and which are contained in the waste in a relatively large number. The broken pieces of glass are then screened and washed with water to remove soil, mud, sand and some paper, cork and plastics. Subsequently the other remaining extraneous pieces and articles such as metal caps and empty cans are manually separated for removal. Undesired magnetic materials are thereafter removed by magnetic separation.
The step of manual separation is indispensable because the extraneous matter other than magnetic materials is difficult to automatically remove. Since the difference in true specific gravity between glass and aluminum is very small and since empty cans, aluminum caps and like pieces engage or embrace pieces of glass and contain air during the breaking step, large quantities of empty cans, caps etc. remaining in the waste glass obtained after washing with water or sink and float separation are cumbersome to manually separate off.
The waste glass separated from the extraneous matter is then crushed to obtain pieces of cullet having sizes in a specified range. Unlike the manual breaking step intended for the removal of extraneous matter, the waste glass must be wholly crushed to a range of effective sizes, e.g. -44 mm to +6.7 mm. In view of efficiency and ease, ore and stone crushers such as jaw crushers and impeller breakers are generally used for this purpose. However, the operation with use of such crushers tends to cause abrasion and compression, consequently breaking up the material excessively to sizes smaller than the desired sizes and yielding a very large amount of fine particles. The cullet obtained will then markedly bubble up when melted in a furnace. In the case where the crushed material is further fed to an optical separator for color separation in order to obtain good cullet, the excessively crushed portion will not be separable depending on the type of the device used, and satisfactory cullet will not be available.